1. Field of the Invention
This invention relates to a radiation sensitive resin composition. More specifically, this invention relates to a radiation sensitive resin composition that is useful in the manufacture of positive and negative type resists suitable for microfabrication using various kinds of radiation. The composition contains a photoacid generator comprising a combination of a compound that generates a carboxylic acid upon exposure to radiation and another compound that generates another acid upon exposure to radiation.
2. Description of Background Art
In the field of microfabrication, as exemplified in the manufacture of an integrated circuit device, a rapidly progressing trend is to establish design rules for products with finer dimensions by the lithographic process with the aim of attaining higher degrees of circuit integration. Development of a lithographic process that is capable of reliably performing microfabrication with precision for a line width of 0.5 .mu.m or less has thus been vigorously pursued in recent years.
The above development also calls for preparation of microfabrication resists with the capability of accurately forming resist patterns with a line width of 0.5 .mu.m or less. However, drawing such a minute pattern with high enough precision is very difficult with the conventional process based on visible rays (wavelength: 700-400 nm) or near ultraviolet rays (400-300 nm). For this reason, lithographic processes based on radiation with a shorter wavelength (300 nm or less) that is capable of achieving a greater focal depth and being effective for establishing design rules for products with finer dimensions have been proposed.
As the lithographic processes using such short wavelength radiation, for example, methods based on a bright-line spectrum of mercury-vapor light (wavelength: 254 nm), a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), X-rays such as synchrotron radiation, or charged particle radiation such as electron beams are being proposed. In addition, a "chemically amplified resist" has been proposed as a high-resolution resist suitable for use with such short wavelength radiation. Improvements in the chemically amplified resist are now being actively pursued.
With a chemically amplified resist, acid is generated when the photoacid generator contained in such a resist is irradiated (a process hereafter termed "exposure"). The acid thus generated acts as a catalyst to trigger chemical reactions such as alteration of polarity, cleavage of chemical bonds, or cross-linking within the exposed part of the resist film. The resulting change in solubility characteristics of the exposed part to a developing solution can then be utilized to develop a pattern.
Various disclosures have been made in the past for such a chemically amplified resist, including resists based on resins wherein (1) an alkali affinitive group in the alkali soluble resin is protected by a t-butyl ester group or t-butoxycarbonyl group (see Japanese Patent Publication No. 27660/1990); (2) an alkali affinitive group in the alkali soluble resin is protected by a silyl group (see Japanese Patent Publication No. 44290/1991); (3) an alkali affinitive group in the alkali soluble resin is protected by a ketal group (see Japanese Patent Application Laid-Open No. 140666/1995); and (4) an alkali affinitive group in the alkali soluble resin is protected by an acetal group (see Japanese Patent Application Laid-Open No. 161436/1990 and Japanese Patent Application Laid-Open No. 249682/1993).
However, it has been pointed out that each of these chemically amplified resists has a peculiar drawback, giving rise to various obstacles for actual application to microfabrication, especially with a critical design dimension of 0.25 .mu.m or less. In most recent years, reports have begun to appear on problems in microfabricating with a critical design dimension of approximately 0.20 .mu.m at a film thickness of 0.5 .mu.m or less. These so-called "nano-edge roughness" or "coating surface roughness" problems are caused by excessive unevenness of the surface and the lateral faces of a resist after pattern formation, hampering microfabrication according to the designed critical dimension.
Meanwhile, concerning radiation sensitive resin compositions of positive as well as negative types, it has been disclosed that line width control can be made easier by using as a photosensitive compound a combination of a photoacid generator and a compound that can be decomposed into a neutral substance upon irradiation (see Japanese Patent Application Laid-Open No. 43837/1997). However, although such a composition excels in resolution, heat resistance, or etching endurance, it has insufficient performance particularly in the matter of "nano-edge roughness" or "coating surface roughness". Therefore, development of a chemically amplified resist that not only exhibits excellent resolution, pattern profile, or other performance but also has the capability of solving the problems of "nano-edge roughness" or "coating surface roughness" is strongly desired.
Accordingly, an object of the present invention is to provide a radiation sensitive resin composition suitable as a chemically amplified resist of either a positive or negative type that effectively responds to various types of radiation such as far ultraviolet rays, X-rays, or charged particle beams. Such a resist is, in addition to having excellent resolution as well as pattern profile, capable of reliably forming highly accurate and minute resist patterns, specifically without causing "nano-edge roughness" or "coating surface roughness".